In brake boosters, such as illustrated in U.S. Pat. No. 4,953,446, a pressure differential is created across a wall that separates a vacuum chamber from a control chamber. The pressure differential acts on the wall to develop an output force corresponding to an input force applied to a control valve. The control valve includes a return spring which urges a plunger toward an atmospheric seat on a poppet member and a seat spring to urge the poppet toward a vacuum seat. The input force is applied to the push rod which compresses the return spring to move the plunger and sequentially allow the seat spring to seat the poppet member on the vacuum seat and the plunger to move away from the poppet member to thereafter allow air to flow to the control chamber. The communication of air through the poppet can effect the uniform development of a pressure differential and as shown in U.S. Pat. No. 4,953,446 a contoured surface could be placed on the push rod to reduce the development of turbulence in the air that is supplied to the control chamber. To further reduce the turbulence in the flow of air and correspondingly noise during a brake application, guides as illustrated in U.S. Pat. No. 5,249,505 could be used for channeling air around a return spring in the valve. Other attempts at reducing noise caused by the flow of air are disclosed in U.S. Pat. No. 4,274,258 where a dust boot has a wall for directing the flow of air and U.S. Pat. No. 4,716,814 where a muffler structure modifies sounds within a valve body.
In analyzing the operation of brake boosters it was observed that air supplied to a control valve most often is obtained from the passenger compartment of a vehicle. If the sounds caused by the flow of air from the passenger compartment during the operation of a brake booster could be shifted from the passenger compartment to an engine compartment a passenger would not hear the booster operation. Unfortunately space in the engine compartment is limited and relocating the brake booster within the engine compartment of a vehicle still requires at least a portion of the components that are associated with a brake booster to remain in a passenger compartment of the vehicle.
In the present invention, a bracket positions a brake booster away from a dash panel and a valve body guard has a cylindrical body through which air from the engine compartment is presented to the valve during the development of an output force in the brake booster to effect a brake application. A resonant chamber within the cylindrical body attenuates noise developed during the flow of air within the brake booster and as a result noise present in the passenger compartment is virtually eliminated.